Process for the conversion of hydrocarbons



Oct. 27, 1970 w.B. BORST, JR

PROCESS FOR THE CONVERSION OF HYDROCARBONS Filed Nov. 8. 1968 mmmox bx 2 Sheets-Sheet l IN VEN TO I? William B. Borst, Jr.

A T TORNE Y5 \mBmI United States Patent US. Cl. 208-61 4 Claims ABSTRACT OF THE DISCLOSURE Combination process for converting, say, black oil into primarily naphtha and gasoline boiling range stock via hydrocracking, hydrogenation, and catalytic cracking.

BACKGROUND OF THE INVENTION This invention relates to the conversion of hydrocarbons. It particularly relates to a combination process for the conversion of black oils into more valuable products, such as naphtha and gasoline boiling range materials.

Petroleum crude oils, particularly the heavy oils extracted from tar sands, topped or reduced crudes, vacuum residuum, etc., contain undesirably large quantities of contaminants, such as sulfur compounds and organometallic complexes and asphaltic materials. These contaminants render the processing of such relatively high boiling point materials exceedingly difiicult, particularly for the conversion of such materials into more valuable lower molecular weight products, such as naphtha and gasoline. As those skilled in the art are well aware, the traditional prior art schemes of handling these heavy materials embody a multitude of processing schemes whereby individual portions of typical charge stocks are separately treated in order to remove these contaminants.

More recently, however, the conversion reaction of hydrogenation, including hydrocracking, utilizing a catalytic composite and hydrogen gas have advanced the art of processing these black oils to the point where distillable hydrocarbons are now achieveable on an economically feasible basis. Such advance has not been achieved, however, without commensurate problems. One of the major problems associated with the hydrocracking of black oils has been that the distillable hydrocarbons obtained from the effluent of the residuum hydrocracking reaction zone are still contaminated with sulfur compounds, metals, and/ or asphaltic materials which render these distillable products unsatisfactory for use in most of the conventional processing schemes associated with these distillable products. For example, additional cracking of heavy gas oil fractions is encumbered by the presence of asphaltic materials which tend to coke up or rapidly deactivate the catalyst used in a distillate hydrocracking process. In addition, the lighter gas oils are generally unsatisfactory for processing through, for example, a catalytic cracking unit because of the metallic contaminant which also rapidly reactivates the catalytic cracking catalyst which is conventionally used in this typical prior art process.

It has now been found that the contaminating materials in black oils may be selectively removed and/or converted in such a manner that the distillable hydrocarbons obtained from black oil hydrocracking may now be processed through conventional subsequent processing treatments, such as distillate hydrocracking, catalytic cracking, catalytic reforming, etc.

SUMMARY OF THE INVENTION Therefore, it is an object of this invention to provide an improved combination process for the conversion of hydrocarbons.

3,536,607 Patented Oct. 27, 1970 "ice It is also an object of this invention to provide a combination process for the conversion of black oil into more valuable products utilizing hydrocracking, hydrogenation, and catalytic cracking.

It is a specific object of this invention to provide a combination process for converting relatively high boiling hydrocarbons into naphtha and gasoline boiling range stocks in a facile and economical manner.

Accordingly, the present invention provides a combination process for converting hydrocarbons which comprises: (a) introducing feed hydrocarbons into a first catalytic reaction zone maintained under conversion conditions including the presence of hydrogen gas; (b) passing the total effluent from said first reaction zone into a first separation zone under conditions sufficient to produce a first vapor stream containing hydrogen and a first liquid stream containing converted hydrocarbons; (c) cooling said first vapor stream to a temperature Within the range from 50 F. to 150 F.; (d) separating the cooled vapor stream in a second separation zone under conditions suflicient to provide a second vapor stream comprising hydrogen suitable for recycle to said first reaction zone and a second liquid stream containing other converted hydrocarbons; (e) passing said first liquid stream into a third separation zone maintained under conditions sufiicient to produce a third vapor stream containing normally gaseous hydrocarbons and hydrogen and a third liquid stream containing converted hydrocarbons; (f) introducing said second liquid stream and said third vapor stream into a fourth separation zone maintained under conditions sufficient to produce a fourth vapor stream comprising normally gaseous hydrocarbons and hydrogen and a fourth liquid stream comprising normally liquid hydrocarbons; (g) passing said third liquid stream into a distillation zone maintained under distillation conditions including subatmospheric pressure sufficient to produce (i) a first fraction comprising light gas oil, (ii) a second fraction comprising medium gas oil, (iii) a third fraction comprising heavy gas oil, (iv) a fourth fraction comprising slop wax, and (v) a bottoms fraction suitable for use as fuel; (h) introducing said light gas oil, said heavy gas oil, and at least a portion of said fourth liquid stream as a combined charge stock into a second catalytic reaction zone maintained under conversion conditions including the presence of hydrogen gas; (i) recovering from said second reaction zone a first product stream comprising converted hydrocarbons; (j) introducing said medium gas oil into a third catalytic reaction zone maintained under cracking conditions in the substantial absence of added hydrogen gas; and, (k) recovering from said third reaction zone a second product stream comprising converted hydrocarbons.

A more specific embodiment of this invention includes the combination process hereinabove wherein said feed hydrocarbons comprise black oil, said first reaction zone conditions include a temperature above 700 F. and a pressure above 1,000 p.s.i.g. sufficient to convert said black oil into lower boiling materials, said second reaction zone conditions include a temperature from 500 F. to 1000 F. and a pressure from to 3000 p.s.i.g. sufiicient to convert said combined charge stock into lower boiling hydrocarbons and said third reaction zone conditions include a temperature below 1100 F. and a pressure below 200 p.s.i.g. sufficient to convert said medium gas oil into gasoline boiling range products.

Therefore, it can be seen that the essence of the present invention involves basically, with respect to black oil processing, a hydrocracking reaction followed by selective separation of the hydrocracking efiiuent into predetermined fractions including a normally liquid fraction containing hydrocracked products. This normally liquid fraction is then separated in a fractionation zone into four separate and distinct boiling range materials; namely, the three gas oils mentioned plus a slop wax fraction which is essential to the satisfactory operation of this combination process. It was found that if the black oil hydrocracking eflluent is separated as taught herein then the light gas oil and heavy gas oil could be blended together and further hydrocracked into naphtha boiling range materials since the Withdrawal of the slop wax fraction effectively removed the asphaltic contaminants from the heavy gas oil fraction, thereby rendering it amenable to further hydrocracking. Similarly, the withdrawal of the heavy gas oil fraction permitted the withdrawal of a medium gas oil fraction which was substantially free of metallic contaminants, thereby rendering the medium gas oil amenable to catalytic cracking or the conversion therein to gasoline boiling range materials. Additionally, it was found that the normally liquid fraction from the cold flash drum could also be satisfactorily blended with the light gas oil and heavy gas oil to make a combined charge stock for further hydrocracking. In other words, the combination process of the present invention permits the conversion of black oil into naphtha and catalytic gasoline as the major liquid product streams. It is to be noted that the slop wax fracton can be recycled to extinction thereby permitting the first catalytic reaction zone to completely convert black oil into essentially distillable hydrocarbons with only a minor amount of residuum passing out of the process as fuel.

DETAILED DESCRIPTION OF THE INVENTION As used herein the term black oil is intended to connote a hydrocarbonaceous mixture of which at least boils above a temperature of about 1050 F. and which has a gravity API at 60 F. of 20.0 or less. This material contains in many instances 60% or more of material boiling above 1050 F. and is considered non-distillable. On the other hand, as used herein distillable hydrocarbons is intended to include those normally liquid hydrocarbons including pentanes having boiling points below about 1050 F. In addition, the phrase hydrocarbons boiling within the gasoline boiling range or gasoline boiling range hydrocarbons is intended to connote those hydrocarbons boiling at temperatures up to about 400 F. or 450 F., including material within this boiling range containing butanes which are present for motor fuel purposes to control the vapor pressure of the gasoline. In similar fashion, the term gas oil is a term of art well known to those skilled in the art. For example, a light gas oil may contain material boiling between 320 F. and 750 F., a medium gas oil may boil substantially within the range from about 750 F. to 980 F. and a heavy gas oil may boil substantially within the range from about 980 F. to 1100 F. These boiling range categories are for illustrative purposes only and those skilled in the art familiar with the term gas oil are well aware that these three major categories may apply to gas oils obtained from a subatmospheric distillation column of the type utilized in the practice of this invention.

Referring now to the first catalytic reaction zone: the

conversion conditions applicable to the processing of relatively high boiling materials through the first catalytic reaction zone include temperatures above about 650 F. with a practical upper limit of about 800 F. at the inlet to they catalyst bed. As those skilled in the art are well aware, the primary reactions taking place through bydrocracking are exothermic in nature so that the reaction zone efiluent will be at a temperature significantly higher than the inlet temperature to the catalyst bed. In order that catalyst stability be maintained, it is preferred to control the inlet temperature at a level so as to maintain the reaction zone effiuent below about 900 F. The operating pressure Will be greater than 1000 p.s.i.g. and,

cubic feet per barrel.

The catalyst used in the first reaction zone is conventional in nature to the extent that it must have hydrogenation activity. Usually, the hydrogenation activity is obtained by having a metallic component composited with a refractory inorganic oxide carrier material of either synthetic or natural origin. Suitable metallic components having hydrogenation activity are those selected from the group consisting of the metals of Groups VIB and VIII of the Periodic Table as indicated in the Periodic Chart of Elements, Fisher Scientific Company, 1953. Included in this group of satisfactory metallic components are one or more components from the group of molybdenum, tungsten, chromium, iron, cobalt, nickel, platinum, palladium, iridium, osmium, rhodium, ruthenium, and avrious mixtures thereof. The concentration of the catalytically active component or components is. of course, dependent upon the particular metal, as well as the characteristics of the feed hydrocarbons which are to be processed through this first reaction zone. For example, with respect to black oil processing, the metallic components of Group VI-B are preferably present in an amount within the range from 1.0% to about 20.0% by weight, the iron group metals in an amount from 0.2% to about 10% by weight and the platinum group metals in an amount within the range from 0.1% to 5% by weight, all of which are calculated as if the components existed within the finished catalytic composite as the elemental metal.

The refractory inorganic oxide carrier material for use in supporting the above-mentioned metallic component are conventional in nature and well known to those skilled in the art. Examples of suitable carrier materials include alumina, silica, zirconia, magnesia, titania, boria, strontia, hafnia, and mixtures of two or more of the above. It is preferred to utilize a carrier material containing at least a portion of silica and, preferably, a composite of alumina, silica, and boron phosphate with alumina being in the greater proportion.

The function of this first reatcion zone is to concentrate a residuum fraction containing sulfur and metallic contaminants while simultaneously producing distillable hydrocarbons. Therefore, the remaining asphaltic materials and heavy sulfur compounds will appear in the slop wax and fuel fractions from the vacuum column. The separation sequence for the hydrocracking reaction zone also concentrates the metallic contaminants in the heavy gas oil fraction and to a lesser extent in the slop wax and fuel fractions.

Referring now to the second reaction zone: suitable conversion conditions within this zone include substantially the same conditions as were maintained in the first reaction zone. However, since the feed material to the second reaction zone is primarily a gas oil material excluding, of course, the medium gas oil fraction, previously mentioned and defined, the reaction conditions may be different. For example, the charge to the second reaction zone in admixture with hydrogen in an amount from about 1000 to about 8000 standard cubic feet per barrel is raised to a temperature within the range from about 500 F. to 1000 F. prior to contacting the catalytic mass. The pressure in the second reaction zone may be maintained from about p.s.i.g. to about 3000 p.s.i.g. with the distillate charge stock contacting the catalytic composite at a liquid hourly space velocity within the range from about 0.5 to about 10.0.

Since the primary purpose of the second reaction zone is to virtually completely remove nitrogenous compounds and sulfur compounds, if any, from the distillate product, a significant degree of hydrocarbon conversion also occurs whereby the heavier molecular weight hydrocarbons, e.g. those boiling at a temperature from about 700 F. to about 1050 F. are converted into lower boiling hydrocarbons, including those in the naphtha boiling range.

' Therefore, the second reaction zone effectively converts the gas oil boiling range material, as preselected, into substantially a naphtha boiling range fraction complemented by normally gaseous hydrocarbon materials and a bottoms fraction suitable for use as fuel.

The catalyst for the second reaction zone may be substantially the same catalyst as was contained in the first reaction zone, although this may not necessarily be required. Preferably, the catalyst in the second reaction zone comprises molybdenum composited on a carrier material of silica and alumina. A typical catalytic composite for utilization in the second reaction zone comprises from 4% to about 45% by weight molybdenum composited with a carrier material of silica and from about 60% to about 78% by weight of alumina. In addition, minor amounts of nickel, say, from about 0.2% to by weight, like quantities of cobalt and/ or iron may be employed in combination with molybdenum for use as the catalyst in the second reaction zone.

The third reaction zone utilized in the practice of this invention includes catalytic cracking conditions in the substantial absence of added hydrogen utilizing a tem perature generally in the range from 600 F. to 1100 F. and a pressure below 200 p.s.i.g. usually from atmospheric pressure to 100 p.s.i.g. The process of catalytic cracking is, preferably, carried out using a fluidized bed technique which is well known to those skilled in the art and need not be described in detail herein. The purpose of the catalytic cracking reaction in the third reaction zone is to convert the medium gas oil fraction, as herein defined and which has substantially no metallic contaminants, into gasoline boiling range products. It is recognized, of course, that the catalytic cracking reaction also produced normally gaseous hydrocarbons in addition to a catalytic gas oil fraction which may be utilized as furnace oil. However, for purposes of this invention, the catalytic cracking reaction will be described as being primarily directed to the conversion of said medium gas oil fraction into gasoline boiling range products.

One of the features which will become evident through the description of the preferred embodiment of this invention presented hereinbelow will be a quench system which is provided to maintain a temperature of the reaction zone efiluent at a predetermined level. As evident from the hereinbelow preferred embodiment, the quench is introduced into the downstream side of the first reaction zone. This term is intended to include the introduction of quench into the lower portion of the catalyst bed, into the lower end of the reactor vessel, and/ or into the transfer line between the reactor vessel and the next succeeding vessel, which normally is the hot high pressure separator. For practical purposes, this term excludes a locus for quench which is introduced into the catalyst bed wherein subsequent reaction is taking place and excludes the introduction of quench directly into the high pressure separator vessel. It is preferable that such quench be introduced into the lower end of the reactor vessel below the catalyst bed to form a physical admixture with the effluent. The utilization of quench in the practice of the preferred embodiment is designed primarily to control the temperature of the first vapor stream from the hot separator. It has previously been found that the temperature of the vapor stream from the high pressure separator immediately following the first reaction zone should be maintained below a temperature of about 800 F., but preferably above a temperature of aout 700 F. but was found that at temperatures of above about 800 F. the heavier normally liquid hydrocarbons carried into this vapor phase thereby considerably contaminating among other streams, the hydrogen gas stream which subsequently is to be recycled to the first reaction zone. In addition, it

was found that the use of this vapor stream with a control point permitted the complete elimination of all other heat exchange equipment between the reactor vessel and the high pressure separator. Therefore, the subsequently separated hydrogen gas is now available for recycle at significantly higher pressures then would be the case for prior art schemes using indirect heat exchange means between the reactor vessel and high pressure separator.

On the other hand, if the temperature of the first vapor stream from this high pressure separator is below about 700 F., ammonia salts resulting from the conversion of nitrogenous compounds contained in the feedstock would tend to contaminate the normally liquid hydrocarbon phase from the bottom of the high pressure separator. If such were allowed to happen, the conventional way of removing these ammonia salts would be by water washing. However, it is presently believed that if an attempt were made to water wash these relatively heavy converted hydrocarbons, an emulsion would be formed by the hydrocarbon and the water, which emulsion would be extremely difficult to break.

One essential feature in the satisfactory practice of the present invention is the operation of the distillation column on the residuum fraction which has concentrated the previously mentioned contaminants. This distillation column is operated at subatmospheric pressure including a pressure from 15 to 100 mm. Hg absolute at the flash zone of the distillation column. Typically, a satisfactory flash zone pressure will be about 25 mm. Hg absolute. Suflicient distillation trays of conventional type must also be present in order to make the requirement selective separation between the various distillable hydrocarbons, including the slop wax fraction. Those skilled in the art familiar with the design of vacuum distillation columns will be able to determine from information present herein the exact physical configuration of the column in order to make the required separation.

Other conditions and operating techniques will be given with the following description of the preferred embodiment of this invention with specific reference to the drawing which is a diagrammatic representation of apparatus for practicing one embodiment of the invention. As will be recognized by those skilled in the art, the embodiment presented by means of flow diagram is simplified as to details. Therefore, details such as pumps, instrumentation and controls, heat exchange.and heat recovery circuits, valving, start-up lines, conventional separation apparatus, and similar hardware has been omitted as being nonessential to an understanding of this invention. The use of such miscellaneous hardware, including conventional separation techniques (not shown), are deemed to be well within the purview of one skilled in the art.

For the purpose of referring to the drawing, it will be assumed that the combination process will be operated with the conversion of a vacuum bottoms stream having a gravity of 60 API at 60 F. and having more than 50% boiling above a temperature of 650 F. This hydrocarbon feedstock also contains about 3.8% by weight sulfur, about 2000 ppm. of nitrogen, about 6.5% by weight pentane-insoluble asphaltic materials, and about ppm. of metals, principally nickel and vanadium.

DESCRIPTION OF THE DRAWING Now with reference to the drawing, the feed material enters the process system through line 1. It is admixed in one instance with slop wax from line 44 produced by vacuum column operation, more fully discussed hereinbelow. The feed material is also admixed with make-up hydrogen of about 97.5 mol percent purity from an external source via line 2. It has been found appropriate in some instances to add water to the reaction zone in admixture with the charge stock. When this is deemed advisable, the water is added via line 3. Normally, however, the use of water is not necessary or desirable.

The hydrogen feed mixture plus slop wax, if any, is further admixed with a hydrogen-rich recycle vapor stream (about 80 mol percent hydrogen) from line 4 and, if desired, a portion of hot liquid recycle from line 40. The total charge, after suitable heat exchange with various streams not shown, is passed through heater 5 to raise the temperature of the charge mixture to about 830 F. In the practice of this embodiment, it is preferred that the heated mixture in line 6 be further admixed with hot recycle stream from line 7 (750 F.) to produce a total reactor charge of about 803 F. and a pressure of about 3100 p.s.i.g.

The total combined feed to the reactor for illustrative purposes may have the following composition based on a commercial size plant:

Component (mols per hour): Line No. 6 520 F.650 F 24.14

NH H O 5.25 N 16.49 H S 637.55 H 8592.91 1221.40 C 168.98 0 89.14 iC 11.12 110 21.07 ic 5.08 nC 4.22 ic 5.00 C 2.03 0 -320" F. 7.05 320 F.520F. 18.76 520 F.-650 F. 24.14 650 F.750 F. 35.28 750 F.980 F. 97.59 980 F.1100 F. 18.91 RESID 49.72

Total 11217.63

Lb./hr. 289,534

Mol wt. 27.81

API

B.p.s.d

The heated feedstock including recycle material in admixture with hydrogen is now passed via line 6 into conversion reactor 8 which contains catalyst disposed therein as a fixed bed; such catalyst being a composite of 2.0% by weight nickel, 16.0% by weight molybdenum on a carrier material comprising 68.0% by weight alumina, 22.0% by weight boron trichloride, and by weight silica. The hydrocarbon phase contacts the catalyst at a liquid hourly space velocity of about 8 based on the original vacuum bottoms or about 2 based on the combined hydrocarbon feed.

The total conversion product effiuent leaves reactor 8 via line 9 in admixture with a hereinafter specified quench stream which has been added to the efiiuent via line 35 at a temperature from about 200 F. to 450 F, typically at about 350 F. Therefore, in line 9 there is the total conversion product efiiuent admixed with the quench stream which has been added via line 35. Prior to the introduction of the quench stream, the conversion product efiiuent is at a temperature of about 875 F. and a pressure of about 3040 p.s.i.g. Sufficient quench is added via line 35 to lower the temperature of the total efiluent stream to less than 800 F. but preferably no lower than 700 F. prior to entering hot separator 10. Typically, the total material entering hot separator 10 will be at a temperature of about 750 F. and a pressure of about 3040 p.s.i.g.

Separator 10 is maintained under conditions sufficient to produce a first liquid stream which is withdrawn through line 11, a portion of which may be diverted via line 40 and a portion of which is diverted through line 7 to combine with the heated mixture in line 6, as previously mentioned. Another portion of this first liquid stream continues through line 11 into hot flash zone 24, more fully discussed hereinbelow. Still another portion of the first liquid stream is passed via line 35 into heat exchanger 38 as the specified quench stream. Further discusion of this material will be presented hereinafter.

A first vapor stream is removed from hot separator 10 via line 12. The temperature of this first vapor stream is measured by temperature recording control device (TRC) 36 which opens or closes control valve 37 in accordance with the deviation of the measured temperature from a predetermined temperature (say, 745 F.) for this first vapor stream. Thus, if the measured temperature in line 12 is 760 F., TRC 36 would open control valve 37 thereby increasing the flow of liquid quench in line 31 in an amount sufiicient to maintain the ultimate temperature of the first vapor stream in line 12 at its predetermined set point of, say, 745 F. After passing the temperature measurement point the first vapor stream passes through condenser 13 whereby the temperature is lowered to about 120 F. with the pressure now being about 3000 p.s.i.g., again due to the pressure drop through the system.

The various streams flowing into and out of hot separator 10 may have the following illustrative composition for a commercial size plant (exclusive of quench material):

Line number 9 11 12 Component, Mols/Hour:

F 10. 80 10. 80 5. 25 5. 25 1. 54 12. 99 17. 67 734. 07 128. 01 7, 329. 94 25. 54 1, 213. 68 6. 95 180. 42 4. 105. 33 0. 69 14. 91 1.44 30. 50 0. 53 9. 31 0. 50 8. 52 O. 97 13. 77 0. 51 6. 62 3. 79 36. 17 14. 52 69. 19. 98 26. 45 27. 74 11. 46 76. 73 3. 49 980 F.-1,100 F. 14. 87 0. 01 RESID 148. 88 39. 09

Total. 11,286. 384. 22 9, 822. 94

416, 62a 82, 698 101, 657 36. 91 215. 25 10. 19. 2 B p.s.d 6,036

It should be noted that the 5 mols per hour of water in the reaction zone efiiuent is water of saturation in the recycle hydrogen stream and/or is Water present in the fresh hydrogen added to the system by means of line 2 and/ or is water carried in with the feed hydrocarbons.

The cooled first vapor stream passes through line 14 where preferably it is admixed with a portion of a fourth liquid stream in line 23 hereinafter described and the resulting mixture is introduced into cold separator 15.

Suitable operating conditions are maintained in cold separator 15 sufiicient to produce a second vapor stream containing about mol percent hydrogen which is removed via line 16, raised to a pressure of about 3380 p.s.i.g. via compressor 17, and passed via line 4 through heat exchanger 38 in indirect heat exchange with the material in line 7 previously mentioned. After'picking up heat through exchanger 38, this hydrogen gas stream passes via line 4 into admixture with the incoming feedstock, as previously mentioned, prior to being introduced into heater 5. If desired, a portion of the hydrogen gas in line 4 may be diverted via line 39 directly into admixture with the incoming feed thereby bypassing heat exchanger 38. Also, as previously mentioned, if Water is added to the feedstock via line 3, then the water may be removed from the system via line 34 from cold separator 15 as indicated on the drawing.

It should be noted at this point that the control of the quench stream is primarily based upon the indirect heat exchange between the hydrogen recycle gas and a portion of the hot separator liquid material flowing in line 7. The control of the amount of liquid quench utilized via line 35 is based upon the temperature measurement of the first vapor stream in line 12 which controls valve 37.

In conjunction with the terminal balance around hot separator 10, the various streams into and out of cold separator 15 may have the following illustrative composition:

Line Number 14 16 18 Component, mols/hour:

Feed

B.p.s.d 7,323

Thus, the second liquid stream (line 18) comprises hydrogen and hydrocarbons boiling for the most part between methane and 1000 F. With a large portion of the material boiling in the gas oil boiling range, say, from 320 F. to 750 F.

Returning now to hot separator 10, the portion of the first liquid stream in line 11 not utilized as recycle or quench enters hot flash zone 24 at a temperature of about 750 F. and is at a substantially reduced pressure of about 100 p.s.i.g. to 500 p.s.i.g., typically, about 250 p.s.i.g. A third liquid stream is removed via line 27, passed through heater 2 8 in line 29 into fractionation column 30 which is maintained under subatmospheric pressure, typically about 25 mm. Hg absolute in the flash zone of fractionator 30. Suitable distillation conditions are maintained in fractionator 30 to produce an overhead vapor stream in line 31 comprising light gases, a light gas oil fraction which is withdrawn via line 32, a medium gas oil fraction whch is withdrawn via line 42, a heavy gas oil fraction which is Withdrawn via line 43, a slop wax fraction which is withdrawn via line 44, and a bottoms fraction suitable for use as fuel which is withdrawn via line 33. Typical operating conditions to produce these various products include a top temperature of 140 F., a top pressure of 10 mm. Hg absolute, the light gas oil is drawnoff at a temperature of 175 F., the medium gas oil is withdrawn at a temperature of 500 F. and a pressure of 15 mm. Hg, the heavy gas oil is drawn-off at a temperature of 650 F. and a pressure of 20 mm. Hg, slop Wax is withdrawn at a temperature of 700 F. and a pressure of 25 mm. Hg, and the fuel fraction is withdrawn at a temperature of 810 F.

Illustrative of commercial operation, vacuum column 30 produces the following stream compositions into and out of column 30:

Line Number- 29 31 32 42 43 44 33 Component, mols/hour:

H 0 -320 F... 320-520 F 520-650 F.- 650-750 F 750980 F.- 9801,100 F. Slop wax--. RES1D--- Total....- 191.78 21.08 45.87 74.03 14.85 6.55 39.09

It is to be noted that the total gas in line 31 going into the vacuum jet system, not shown, contains a small amount of condensable material which is, preferably, recovered by conventional means, not shown, and utilized as an additional feed stream to the second reaction zone, more fully discussed hereinafter.

Returning now to hot flash zone 24, a third vapor stream is removed therefrom via line 2-5, is cooled and condensed to about 125 F. in condenser 26, and then passed into cold flash separator 20 through line 19; how ever, it is to be noted that the cooled third vapor stream is preferably combined with the second liquid stream in line 18 from cold separator 15. The total material entering cold flash separator 20 via line 19 is at a pressure of about 225 p.s.i.g. and a temperature of about F.

Suitable conditions are maintained in cold flash zone 20 to produce a fourth vapor stream comprising normally gaseous hydrocarbons and acid gases, such as H 8 and hydrogen. This gaseous stream is removed from the separator 20 via line 21. Since this material in line 21 contains a considerable quantity of hydrogen sulfide, it is generally subjected to a suitable treating process prior to being vented, burned as fuel, or passed into an absorber system for the recovery of hydrocarbons therefrom. The particular economic aspects to be considered will dictate Whether the fourth vapor stream (line 21) is suitably treated to recover the small quantities of hydrocarbons contained therein. A liquid stream comprising normally liquid hydrocarbons is removed from cold flash zone 20 via line 22 and a portion thereof is diverted through line 23 to be combined with the cold first vapor stream in line 14 thereby forming the total feed stream to cold separator 15, as previously mentioned. The remaining amount of fourth liquid stream is passed via line 41 into admixture with selective fractions from fractionator 30 and processed further in a manner discussed hereinafter. For illustrative purposes, the materials into and out of cold ll flash zone 20 will have the following typical composition Line Number 21 22/41 Component, mole/hour:

Fem

Returning now to fractionator 30 and the products separated therefrom, the material in line 41 which contains a considerable amount of gas oil material concentrated primarily in the light gas oil fraction is mixed with the light gas oil in line 32, passed via line 46 into admixture with the heavy gas oil fraction in line 43, and then subsequently passed via line 47 and 49 into second catalytic reaction zone 50. Added hydrogen necessary for the hydrocracking reaction in reactor 50 is introduced via line 48. Typical operating conditions maintained in second reaction zone 50 include a combined feed inlet temperature of about 775 F. under an imposed reactor pressure of 2600 p.s.i.g. The total effluent is withdrawn from reactor 50 via line 51 at a temperature of about 875 F. and a pressure of 2550 p.s.i.g. and introduced into separation zone 52. Hydrogen gas suitable for recycle to the second reaction zone is withdrawn from separator 52 via line 53, admixed with the incoming feed stream and returned to reactor 50 in the manner previously discussed.

The liquid hydrocarbon stream is withdrawn from separator 52, passed via line 54 into fractionator 55 for the separation therein of lower boiling hydrocarbon materials, namely, a gaseous hydrocarbon stream which is withdrawn via line 56 and a naphtha stream which is withdrawn via line 57. A residual amount of bottoms material is Withdrawn from the second reaction zone processing train via line 58 and is preferably utilized as fuel.

One of the features associated with the processing through reactor 50 is that combined hydrocarbon feed in line 49 is substantially free of asphaltic material. One of the essential features in the practice of this invention is the utilization of a slop wax cut which effectively withdraws from the system any asphaltic materials which were concentrated in the residuum fraction previously separated and present in line 27.

The remaining material to be processed is the medium vacuum gas oil stream which was removed from fractionator 30 via line 42. The predetermined and selective separation of a light gas oil fraction above and heavy gas oil fraction below this selected draw-01f stream effectively renders the medium gas oil substantially metallic-free so that it is uniquely suitable for processing in catalytic cracking reactor 62 which is of the conventional fluidized bed configuration.

As those skilled in the art are well aware, the medium gas oil is passed via line 42 into the base of reactor riser 61 where hot catalyst, such as silica-magnesia, from re generator enters the riser from line 60. If necessary, auxiliary charge, such as gas oils from other sources may be introduced into the catalytic reaction zone or third reaction zone via line 59. The mixture of hot catalyst and oil passes via riser 61 into reactor vessel 62 wherein the catalyst is separated from the oil vapors and returned via line 64 into regenerator 65 for regeneration therein utilizing techniques well known to those skilled in the art. The hydrocarbon vapors which have been cracked pass out of reactor 62 via line 63 which contains several vessels, including a main column for the separation of the cracked vapors into conventional products.

As previously mentioned, the purpose of the third reaction zone illustrated by reactor 62 is the production of catalytic gasoline which is withdrawn from separator 66 via line 67. It is recognized that there are other products which may be separated in zone 66, namely, cycle oil and normally gaseous hydrocarbons which have not been shown in order to simplify this diagram. It is to be noted that one of the essential features of this invention is the discovery that fractionator 30 operating on a feedstock in line 29 which has been judiciously selected produces a medium gas oil fraction substantially free of metallic compounds so that it can be processed eflFectively through catalytic reaction zone 62.

Therefore, it can be seen from the above specific and illustrative embodiments that the present invention provides a combination process for converting a relatively heavy hydrocarbon feedstock into essentially gasoline and naphtha in a facile and economical manner utilizing a specific separation scheme operating in conjunction with three reaction zones which complement each other.

The invention claimed:

1. Combination process for converting hydrocarbons which comprises:

(a) introducing feed hydrocarbons into a first catalytic reaction zone maintained under conversion conditions including the presence of hydrogen gas;

(b) passing the total effluent from said first reaction zone into a first separation zone under conditions sufficient to produce a first vapor stream containing hydrogen, and a first liquid stream containing converted hydrocarbons;

(c) cooling said first vapor stream to a temperature within the range of 50 F. to F.;

(d) separating the cooled vapor stream in a second separation zone under conditions suflicient to provide a second vapor stream comprising hydrogen suitable for recycle to said first reaction zone, and a second liquid stream containing other converted hydrocarbons;

(e) passing said first liquid stream into a third separation zone maintained under conditions sufiicient to produce a third vapor stream containing normally gaseous hydrocarbons and hydrogen, and a third liquid stream containing converted hydrocarbons;

(f) introducing said second liquid stream and said third vapor stream into a fourth separation zone maintained under conditions suflicient to produce a fourth vapor stream comprising normally gaseous hydrocarbons and hydrogen, and a fourth liquid stream comprising normally liquid hydrocarbons;

(g) passing said third liquid stream into a distillation zone maintained under distillation conditions including subatmospheric pressure sufficient to produce (i) a first fraction comprising light gas oil,

(ii) a second fraction comprising medium gas oil, (iii) a third fraction comprising heavy gas oil, (iv) a fourth fraction comprising slop wax, and, (v) a bottoms fraction suitable for use as fuel;

(h) introducing said light gas oil, said heavy gas oil, and at least a portion of said fourth liquid stream as a combined charge stock into a second catalytic re action zone maintained under conversion conditions including the presence of hydrogen gas;

(i) recovering from said second reaction zone a first product stream comprising converted hydrocarbons;

(j) introducing said medium gas oil into a third catalytic reaction zone maintained under cracking conditions in the substantial absence of added hydrogen gas; and,

(k) recovering from said third reaction zone a second product stream comprising converted hydrocarbons.

2. Process according to claim 1 wherein said feed hydrocarbons comprise black oil, said first reaction zone conditions include a temperature above 650 F. and a pressure above 1000 p.s.i.g. sufficient to convert said black oil into lower boiling materials, said second reaction zone conditions include a temperature from 500 F. to 1000 F. and a pressure from 100 to 3000 p.s.i.g. suflicient to convert said combined charge stock into lower boiling hydrocarbons, and said third reaction zone conditions include a temperature below 1100" F. and a pressure below 200 p.s.i.g. sufiicient to convert said medium gas oil into gasoline boiling range products.

References Cited UNITED STATES PATENTS 1/1966 Williams et al 20860 9/1962 Honerkamp et al. 20861 DEL-BERT E. GANTZ, Primary Examiner A. RIMENS, Assistant Examiner US. Cl. X.R. 208--60, 251, 254 

